Many vehicles now utilize hybrid-electric powertrains in order to increase the efficiency of the vehicle. A hybrid-electric powertrain typically involves an internal combustion engine that operates a generator that produces electrical power that may be used to drive electric motors used to move the vehicle. The electric motors may be used to provide power to wheels of the vehicle to move the vehicle, or the electric motors may be used to supplement power provided to the wheels by the internal combustion engine and a transmission. In certain operational situations, the electric motors may supply all of the power to the wheels, such as under low speed operations. In addition to providing power to move the vehicle, the hybrid-electric powertrain may be used to power a PTO of the vehicle, sometimes also referred to as an electric PTO or EPTO when powered by a hybrid-electric powertrain, that in turn powers PTO driven accessories.
In some vehicles, such as utility trucks, for example, a PTO may be used to drive a hydraulic pump for an on-board vehicle hydraulic system. In some configurations, a PTO driven accessory may be powered while the vehicle is moving. In other configurations, a PTO driven accessory may be powered while the vehicle is stationary and the vehicle is being powered by the internal combustion engine. Still others may be driven while the vehicle is either stationary or traveling. Control arrangements are provided for the operator for any type of PTO configuration.
In some PTO applications, the vehicle's particular internal combustion engine may be of a capacity that makes it inefficient as a source of motive power for the PTO application due to the relatively low power demands, or intermittent operation, of the PTO application. Under such circumstances, the hybrid-electric powertrain may power the PTO, that is, use of the electric motor and generator instead of the IC engine to support mechanical PTO, may be employed. Where power demands are low, the electric motor and generator will typically exhibit relatively low parasitic losses compared to an internal combustion engine. Where power demand is intermittent, but a quick response is provided, the electric motor and generator provides such availability without incurring the idling losses of an internal combustion engine.
Many hydraulic systems contain a plurality of hydraulic circuits, such that multiple hydraulically operated components may be present. Each of the plurality of hydraulic circuit typically has a dedicated hydraulic pump to provide hydraulic fluid pressure to the hydraulic circuit. These hydraulic systems typically comprise a combination valve that allows hydraulic fluid from one hydraulic circuit to be diverted to another hydraulic circuit if heavy hydraulic loading conditions are present within one of the circuits. Therefore, if the demand for hydraulic pressure within one of the circuits is more than the hydraulic pump for that circuit is capable of generating, the combination valve will allow hydraulic fluid from a different hydraulic circuit to enter the hydraulic circuit that requires additional hydraulic pressure.
Many times a combination valve will active before a hydraulic circuit actually requires additional hydraulic pressure, and excessive backpressure may be generated in the hydraulic circuit that is having hydraulic fluid from another circuit diverted into it. This excessive backpressure may result in excessive wear or damage to the hydraulic system including the hydraulic pump. Additionally, the premature operation of the combination valve results in additional torque to be supplied to the hydraulic pump of the circuit having hydraulic fluid diverted from it, resulting in additional demand placed on the engine or the electric motor and generator. This is particularly inefficient when the hydraulic circuit receiving hydraulic fluid from another circuit does not require that additional fluid, as the additional power from the engine or the electric motor and generator does not result in any useful work being performed by a hydraulically driven component. Therefore, a need exists for a control system for a hybrid-electric powertrain that evaluates a load on a hydraulic circuit prior to activating a combination valve.
Conventionally, once a hybrid electric vehicle equipped for EPTO enters the EPTO operational mode, the electric motor and generator remains unpowered until an active input or power demand signal is provided. Typically, the power demand signal results from an operator input received through a body mounted switch which is part of data link module. Such a module could be the remote power module described in U.S. Pat. No. 6,272,402 to Kelwaski, the entire disclosure of which is incorporated herein by this reference. The switch passes the power demand signal over a data bus such as a Controller Area Network (CAN) now commonly used to integrate vehicle control functions.
A power demand signal for operation of the traction motor is only one of the possible inputs that could occur and which could be received by a traction motor controller connected to the controller area network of the vehicle. Due to the type, number and complexities of the possible inputs that can be supplied from a data link module added by a truck equipment manufacturer (TEM), as well as from other sources, issues may arise regarding adequate control of the electric motor and generator, particularly during the initial phases of a product's introduction, or during field maintenance, especially if the vehicle has been subject to operator modification or has been damaged. As a result, the traction motor may not operate as expected. In introducing a product, a TEM can find itself in a situation where the data link module cannot provide accurate power demand requests for electric motor and generator operation for EPTO operation due to programming problems, interaction with other vehicle programming, or other architectural problems.